1. Field of the Invention
The present invention relates to a stainless-steel seamless belt for use in a base material of a fixing belt for use in a heat fixing apparatus of an electrophotographic image forming apparatus, and a manufacturing method therefor. In addition, the present invention relates to a fixing belt and a heat fixing apparatus for use in the electrophotographic image forming apparatus.
2. Description of the Related Art
The electrophotographic image forming apparatus uses a heat fixing apparatus for fixing an unfixed toner image on a recording material surface.
Recent heat fixing apparatuses use a power-saving ceramic heater as a heat source to heat a resin belt or a metal belt with a small heat capacity. FIG. 2 schematically illustrates an example of the heat fixing apparatus. In the heat fixing apparatus illustrated in FIG. 2, a heat-resistant belt (fixing belt 33) is interposed between a ceramic heater 31 as a heat source and a pressure roller 35 as a pressure member to form a fixing nip portion 36. In the fixing nip portion 36, a recording material P bearing an unfixed toner image T to be subjected to heat fixing is introduced between the fixing belt 33 and the pressure roller 35. The recording material P is conveyed with being sandwiched between the fixing belt 33 and the pressure roller 35. Thus, in the fixing nip portion 36, heat of the ceramic heater 31 is transmitted to the recording material P through the fixing belt 33. The heat and the pressure allow the unfixed toner T on the recording material P to be fixed to the recording material P. In FIG. 2, the heat fixing apparatus further includes a belt guide member 32 and a pressurizing rigid stay 34.
Examples of materials of the fixing belt for use in such a heat fixing apparatus generally include a heat-resistant resin, and particularly include a polyimide resin excellent in heat-resistance and strength. Unfortunately, with a recent improvement in process speed, the resin fixing belt has insufficient thermal conductivity. In other words, it may be difficult to fix an unfixed toner image to a recording material in a short time and in a sufficient manner. In light of this, there has been proposed that the fixing belt is provided with a base layer containing a metal excellent in thermal conductivity such as stainless steel, nickel, aluminum, and copper (see Japanese Patent No. 3970122).
Japanese Patent No. 3970122 describes a method of manufacturing a stainless base layer. Specifically, the following method is described as a first embodiment.
First, a step is performed of obtaining a cup-shaped stainless cylindrical member (a first-stage metal tube) by subjecting a stainless metal flat plate to a deep-drawing process a plurality of times. Next, a step is performed of obtaining a seamless belt (a second-stage metal tube) by cutting a cup base portion by performing an ironing process using a general spinning drawing process to form a stainless cylindrical member with a predetermined thickness or by performing an ironing process using a continuous die while rotating the first-stage metal tube. Finally, a metal belt of a desired inverted crown shape (a third-stage metal tube) is obtained by subjecting the second-stage metal tube to a hydraulic bulge forming process followed by internal pressure load and plastic forming processes.
Further, as a second embodiment, there is proposed a manufacturing method which includes obtaining a metal belt by performing a complete annealing process at 800° C. to 1,100° C., between the steps of obtaining the second-stage metal tube and the third-stage metal tube according to the first embodiment.
Furthermore, as a third embodiment, there is proposed a method which includes obtaining a metal belt of an inverted crown shape (a third-stage metal tube) by controlling the pressure and the speed at the spinning drawing process in the step of obtaining the second-stage metal tube according to the first embodiment.